1. Field of Invention: The present invention relates to isolating the energy generated by shear wave seismic vibrators from their transport vehicles.
2. Description of Prior Art:
Prior art seismic shear wave vibrators have been used to impart energy to the earth by a horizontally vibrating mechanism reacting against a baseplate firmly coupled to the earth. The equal and opposite reaction of the baseplate is transmitted to the earth to form shear waves for exploration. So far as is known, these shear wave vibrators requird that their transporting vehicle apply a portion of its weight as a compressive, or hold-down, force to the base plate during seismic operations. The application of this hold-down force was used to help to improve the coupling of the baseplate to the earth. An example of this type of system is set forth in U.S. Pat. No. 4,143,736.
In these systems, however, the hold-down force was applied to the top of the baseplate in a vertical direction. Typically, air bags were attached extending vertically at their opposite ends between the transporting vehicle and the baseplate in an attempt to isolate the vertical compressive force from the horizontal vibration. However, as the baseplate vibrated horizontally, the air bags were subjected to shear forces. Since the air bags were mounted vertically, their primary compliant direction was in the vertical plane and there was limited compliance of the air bags in the horizontal direction. The resultant horizontal shearing action on the air bags during vibration was detrimental to their service life. It was also a difficult and involved process to remove and replace these air bags when they failed due to shearing forces.